I bought myself a LC meter. what to make of the numbers? lol

Pumpkinguy

Member
I've tested a couple motors with bell off.
Here are the numbers. Can you guy please explain what I'm looking at?

Motor 1: 17.59uh, 17.58uh, 16.85uh
Motor 2: 17.51uh, 17.71uh, 17.43uh
Motor 3: 18.34uh. 18.16uh, 17. 88uh

Thanks.
 

econfly

Member
It's giving you an inductance measure in microhenries.

http://en.wikipedia.org/wiki/Inductance

http://en.wikipedia.org/wiki/Henry_(unit)

Your meter probably can also measure resistance on the same circuit. Many LCR meters have an auto-detect mode that tries to determine if the device under test is a resistor, capacitor, or inductor and then the meter defaults to its best guess of what to measure.

I don't have a good answer for what values you should expect for uH if testing a pair of motor leads -- would have to give that some thought. I would guess that the same make/model of motor should show consistency for any given measurement, but that's obvious enough.
 

Pumpkinguy

Member
From what I understood before ordering this was that the inductance number, whatever that may be should be fairly close across each of the 3 coils in a brushless motor. Numbers vastly different would indicate a short somewhere. I guess what I'm asking here is what is acceptable and what is not? Is it a percentage difference that would indicate a problem?

Thanks.
 

econfly

Member
I would start with the meter data sheet and find the typical measurement error. If you see differences outside the error range (and this will be at a given frequency of measurement -- which is best I don't know) then go from there. Fundamentally we should have some understanding of the desired level, but honestly I don't have a clue right now.
 



cootertwo

Member
I bought a multimeter that will do those measurements, also after watching that video, but haven't tried it yet. It would be interesting to test a handful of motors, and see how much of a difference there is. BTW, what are you using to remove those damned iddy biddy circlips ????
 


Inductance in brushless motors is ... complicated. Using an LC meter like this on brushless motors is of little practical use, in my opinion. They usually give inductance values that are too low. For what you are doing I guess it is fine, although it would be better just to use a low resistance measurement method (4-wire, Kelvin connection) to check the line-to-line resistance.

If you want to use it as a sanity check to make sure the windings are similar, I think that's probably okay. If you are seeing +/-10% difference in your measurements (which you are), you should be okay. But, like I said, they usually give you too low of a measurement.
 

Pumpkinguy

Member
Inductance in brushless motors is ... complicated. Using an LC meter like this on brushless motors is of little practical use, in my opinion. They usually give inductance values that are too low. For what you are doing I guess it is fine, although it would be better just to use a low resistance measurement method (4-wire, Kelvin connection) to check the line-to-line resistance.

If you want to use it as a sanity check to make sure the windings are similar, I think that's probably okay. If you are seeing +/-10% difference in your measurements (which you are), you should be okay. But, like I said, they usually give you too low of a measurement.

That's a good answer. Thank. I figured there was no way other than luck that they would be the same. These things are hand wound from my understanding.
It was a $30 tool I thought would come in handy. Lol
 

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